Voltage regulated power device



April 2, 1963 A. KALE'NIAN 3,084,317

VOLTAGE REGULATED POWER DEVICE Original Filed DeC. 15, 1958 2Sheets-Sheet 1 V kvc lllllllllllllllllllllllllll I l l2 1/ N Iv INK x6 FT E 14 M l 1 t v Flg. l

Fig. 3

IN VEN TOR. ARAM KALENIAN BY gmmum rsw,wnm a z-mvna'zm ATTORNEYS April2, 1963 A. KALENIAN lllllllllllllllllllllllll VOLTAGE REGULATED POWERDEVICE ZSheets-Sheet 2 IR! Fig. 4

N turns Fl 5 9 N turns N iurns I! I00 I I 75 v (Volts) V 50 \1 i a O I(Amperes) INVENTOR.

ARAM KALENIAN BYmwm mum, mm. & mumtm ATTORNEYS United States Patent 19Claims. (Cl. 318-245) The present invention relates generally to motorcontrol devices. More particularly, it relates to means including amotor and a circuit for connection of the motor to a source ofalternating-current supply voltage, this circuit being adapted to varythe power supplied to the motor in a predetermined manner as a functionof an applied load. This application is a continuation of my copendingapplication Serial No. 780,322.

The principal object of this invention is to provide an automatic meansto vary the voltage across the power device in a predetermined manner asa function of the applied load. In motor applications where constantspeed is desired, the voltage is automatically and instantly varied bythe amount required to overcome the tendency of machines to slow downwith load and to preclude overspeeding when the load drops off abruptly.

A further object is to provide the foregoing results by means ofcircuitry having stable characteristics, whereby transitions in thevalue of the load effect smooth transitions in the variable parameterswithout instability, momentary overspeeding or other transientphenomena.

With the foregoing and other objects in view, the present invention hasas its principal feature the provision of an inductance and acapacitance connected in series with a power device, the inductancehaving a saturable core.

Another feature resides in the selection of values for the variouscircuit parameters in relation to the characteristics of the given powerdevice, including its elfective impedance, its speed and the range ofvoltage regulation required to maintain a desired speed variation withload between specified limits.

Other features reside in certain features of the circuit and incharacteristics of the elements thereof which will become clear from thefollowing description of certain preferred embodiments, having referenceto the appended drawings, in which FIG. 1 is a schematic diagram of acircuit embodying the invention as applied to a series-woundalternatingcurrent motor; to run it at one pre-selected reasonablyconstant speed over the full range of no load to full load;

FIG. 2 is a vector diagram illustrating the response of various circuitparameters of FIG. 1 to a change in load conditions according to theinvention;

FIG. 3 is a schematic circuit diagram illustrating a variation in thecircuit of FIG. .1 for speed regulation of a series direct-current typemotor operating from an alternating current power source;

FIG. 4 is a schematic diagram of a circuit embodying the invention asapplied to an independently-excited direct-current motor; and

FIG. 5 is a graph illustrating the impedance characteristics of thesatur-able core inductance according to the invention.

Referring to FIG. 1, there is illustrated a commutatortype alternatingcurrent motor M having an armature A and a series field winding F. Themotor and other elements hereinafter described are connected in acircuit across terminals 12 energized by a variable voltage trans.-former T (shown as an auto-transformer) connected to analternating-current power supply source. The voltage applied to themotor circuit is designated E. It is assumed that this voltage E remainssubstantially constant Patented Apr. 2, 1963 under varying loadconditions of the motor M for a given selected speed of operation. Inseries with the motor M are connected a capacitance C and asaturable-core inductance L. The core of the inductance L issubstantially fully saturated for all values of current throughout theno-load to maximum-load range of the motor. The preferred core materialis one having sharp saturation characteristics as shown in FIG. 5 andherein-after more fully described.

Inductances having sharp saturation characteristics are well-known inthe art, and the intention herein is to refer to the various formsthereof generally.

As is well-known in the art, when a constant voltage source is connecteddirectly to a typical series motor the latter has a drooping speed-loadcharacteristic, that is, the speed decreases considerably as the appliedload increases. However, when this type of motor is connected in theabove-described circuit with constant voltage E, a different speed-loadcharacteristic results. This may be explained by reference to FIG. 2which is a vector diagram illustrating the various voltages identifiedin FIG. 1. It will be understood that this diagram is an approximationbased on the assumption that the waveforms are sinusoidal. In practicalapplications, the waveforms often depart to a certain extent from a puresine wave; but the illustrated principle of operation is generallyapplicable. The solid black vectors indicate the condition for a firstassumed load. The vectors drawn in broken lines indi cate thecorresponding conditions resulting from a speci fied increase in theapplied load.

Referring first to the conditions indicated by the solid lines, theapplied voltage E equals the vector sum of the voltages across theinductance L, the capacitance C and the motor M, represented by voltagesV V and V respectively. The inductive reactances in the circuit aresubstantially greater than the capacitive re-actance, with the resultthat a current I flows in lagging relationship to the voltage E. Thephase angle of the voltage E to the current I is indicated by a.

The motor M has :a resistive-inductive effective impedance in thecircuit, the in-phase or apparent resistive component being largerelative to the inductive reactance. Therefore, the current lags thevoltage V by a relatively smaller angle b.

The voltage V leads the current I by nearly degrees and the voltage Vlags the current I by 90 degrees. (These conditions are substantiallyrealized in the case of practical capacitances, but ordinarily apractical inductance includes a relatively small inherent ohmicresistance. For simplicity in this explanation, this ohmic resistance isassumed to be negligible.) The vector sum of the voltages V and V (whichsum is approximately the difference between their absolute values), addsvectorially to the voltage V to produce a sum equal to the appliedvoltage E.

Next assume that the applied load increases. The resulting circuitconditions are then represented by the broken vector lines. The appliedvoltage E remains equal in magnitude to the original voltage E. Sincethe core of the inductance L was substantially fully saturated under theoriginal conditions the flux through the core increases but slightly,and therefore the magnitude of the voltage V;, increases but slightly tothe value V The voltage drop V on the other hand, increases to V indirect proportion to the increase in current I to I.

The foregoing changes result in a smaller phase angle a between theapplied voltage E and the current I, with voltage vectors V and V inquadraturewith the new current I. It will be noted from FIG. 5 thatwhile the voltage V has increased but slightly, the voltage V hasincreased more substantially. The voltage across the motor M increasessubstantially as shown by the vector V By appropriate selection ofvalues for the parameters L and C, this increase in applied voltageacross the motor is just sufficient to cause the speed of the motor toremain at or close to its original value.

Certain further observations may be made from FIG. '2. For example, itwill be noted that the substantial increases in V with increasing loadas noted above result from the fact that V increases but slightlythroughout the current region of interest, the values of V and V bothincreasing substantially in magnitude to reach the value of the supplyvoltage E by vector addition. The type of inductance which bestsatisfies this condition is one which has a so-called sharpcharacteristic, that is, one which has a substantial current range inwhich the rise in voltage is small and nearly linear.

A further understanding of the procedure for utiliza- 'tion of thisinvention and the phenomena discussed above may be gained by referenceto FIG. which shows the voltage-current characteristic of a typicalinductance L 'for each of three tapconnections on the latter. The numberof turns N included in the circuit tor each curve are indicated as Nturns, N turns and N turns, respectively. Taking for example the curvefor N turns, it is seen that up to one ampere the voltage across theinductance rises steeply, while for currents between one and amperes thevoltage increases only over the range from approximately 125 to 135volts, indicating substantially complete saturation of the core of theinductance in this latter range. For efiective operation with N turns ofthe inductance in circuit, the current range from no-load tomaximum-load for the motor falls entirely within the saturated range.

For different numbers of turns connected in the circuit, similar curvesare obtained, as indicated for N and N but at different voltage levels.In any case there is substantial saturation over a wide range ofcurrent.

For any given desired speed, the variable inductance L and thetransformer T are placed on particular settings. The selected speed maybe changed by varying L and E simultaneously. For maximum speed both theinductor L and the transformer T will include the maximum num ber ofturns, while for lower selected speeds the number of turns on both willbe reduced. In FIG. 2 the reduction of applied voltage has the effect ofmaking the locus of E a smaller circle, and also making V smaller for agiven current; The general characteristics of the circuit are retained,however, and the same desired condition of constant speed over a widerange of load is retained.

For convenience in operation, the variations in L and E are preferablyobtained by a single control, illustrated by the mechanical connection14 in dash lines. It has been found that a simple connection giving alinear relation between the numbers of turns on L and T will affordSubstantial constancy of speed versus load for any setting.

The actual choice of values will depend on the actual Workingconditions, but the description thus far given will enable one skilledin this art to select parameters for satisfactory regulation. Forexample, let it be assumed that the system is to be designed forconstantspeed operation of a motor driving a load having a knownspeed-torque characteristic. The speed and torque characteristics of themotor as functions of current will also be known, and the requiredvalues of V for two separated values of load current can be determined(e.g". light load and full load). An inductor will be chosen that willbe saturated, as shown in FIG. 5 for both of these values of loadcurrent. The voltage V will rise somewhat over the range because thesaturation is not complete. The condenser size will then be determinedin a manner to reduce the quantity V -V to a value to conform generallyto the vector diagram. of FIG. 2. There is some freedom in the choice ofL and C, but as [Terminal voltage (across terminals 12)115 volts] I V1.V0 VL-VC VM R.p.m.

It will be seen that the actual voltage applied to the motor ranges overabout 35 volts, while voltage V -V has a range of 53 volts. This voltageV V is the voltage subtracted from the line voltage by the controlcircuit, and if the phase angle between line and motor voltage werezero, its range would be the same as the range for V The phase angle,however, requires a larger range for V -V Except for the light-loadcondition, the speed is exceptionally constant over a nearly 4-to-1range of load current.

When the motor is to be operated at various set speeds by using thevariable inductor and transformer T, similar relations may be found forthe different speeds, and it will be found that a linear or nearlylinear relationship exists between the terminal voltage and the voltageV It is therefore possible to connect the drives for transformer T andthe inductor L together by simple gearing or other suitable mechanism(shown diagrammatically at 14) to provide a unitary control.

The condenser C, although shown as variable, will usually provideexceptionally good speed regulation under all conditions even if ofconstant value. The variable feature may be omitted, except where tineadjustment of speed under Widely varying loads may be desired.

A feature of this invention is that the circuit inherently tails safe.That is, if the condenser forms a shortcircuit for any reason, theseries inductance stops or retards the flow of current and the motorstops. Likewise, if the inductance develops an open circuit, no currentflows through the circuit.

The foregoing description assumes that the motor M is of thealternating-current type. If desired, I may employ a series-wound directcurre'nt motor and obtain results similar to those described above. Inthis case the circuit of FIG. 3 is substituted for the motor M betweenthe terminals T and T in FIG. 1. A bridge rectifier R supplies the motorwith unidirectional current. In other respects the operation issubstantially the same as that described above for analternating-current motor and the vector diagram of FIG. 2 is generallyapplicable. It will be understood that this form of rectifier isintended merely as exemplary, and other well-known rectifier circu'itsmay be used equally well, the choice depending on convenience and otherpractical considerations.

Another embodiment of the invention is illustrated in FIG. 4. Aseparately-excited direct-current motor M has its armature A connectedacross a bridge rectifier R which is connected in series with aninductance L and capacitance C in a manner similar to the motor M ofFIG. 3. The field winding F is excited in a conventional manner by adirect current, preferably obtained by rectifying an alternating voltageB; through another full-wave bridge rectifier R Although the systems ofFIG. 1 and FIG. 4 operate on similar principles in that an increase inload current produces an increase in voltage across the motor, there aresome differences.

Since the field excitation does not change with load, the system of FIG.4 will, in general, require a smaller range for V for a given range ofload. Thus, in the numerical example given above for FIG. 1, wherein therange for V was about volts, the corresponding range for the examplegiven below for FIG. 4 system is about 23 volts for the power range of33% to 133% Since the field coil in the FIG. 4 system is not in serieswith the armature but is independently excited, a change in armaturecurrent is not accompanied by a change in field current. Also since thefield is not in series, there is no inductive voltage drop due to thefield coil and the armature gets the full benefit of the change in V Ittherefore sufiices to vary the inductance L only without changing theterminal voltage; or to hold the inductance constant and change theterminal voltage only in order to go from one speed setting to another.I

Another difference is that the condenser in FIG. 4 will be, in general,larger in value than in FIG. 1 for the reason that a smaller range of Vwill sufiice to keep the motor at reasonably constant speed over theentire range from no load to full load or even a substantial overload.Thus, in the numerical example previously given for the FIG. 1 system,the value of C is about 300 mfd.; but in the separately excited motorsystem, the value of C ranges from 275 mfd. at the lowest speed range to375 mfd. at the highest speed range. It can be observed from this thatthe greater the voltage change needed to keep the motor at constantspeed over the load range, the smaller the value of C; and conversely,the smaller the voltage change required, the greater the value of C.

In the FIG. 4 system, variation of the desired speed may be obtainedsimply by varying inductance L only which in turn changes basic armaturevoltage. For extreme ranges of speed both the field current and theinductance L may be varied. Variation of the field current may be donein any suitable Way, as by the use of a series resistor 20 shown in thedrawing, or by varying the voltage E with a variable transformer.

The value of C, which determines the range of V has a reasonable degreeof latitude and may be kept constant over the entire speed range with areasonably close control of speed over the entire power range of themotor. However, if speeds must be held critically close to apredetermnied setting over the range of no load to a substantialoverload, it may be desirable to vary the value of C to yield thenecessary V for this purpose.

Since the FIG. 4 system has inherently a dual range of speed control,i.e., armature control by varying inductance L and field control byvarying voltage to the field coil, it is possible to obtain, in smoothand infinitely small steps, a speed change in the ratio of :1 or more,and for each speed setting substantially constant speed will be obtainedover a load range of nearly no load to considerable overload.

Typical test results on a separately excited H.P. motor having a basespeed of 850 r.p.m. and rated full load current of 7.46 amperes are asfollows:

[Terminal voltage280 volts A.C. Field-120 volts 13.0.]

I Vr. V0 VIr-VC VM (D.C.) R.p.m.

6 and load characteristics of the above-mentioned A HR motor, withpreferred values of capacitance. Field vo1tage is 120 volts D.C. exceptas noted.

Rpm R.p.m., R.p.m., Rpm R.p.rn., No Load Mfd 2.5 5.0 7.5 10.0

Amps Amps. Amps. Amps 1 90 volt A.O. Field-rectified. 2 60 volt A.O.Field-rectified. B 30 volt A.G. Fieldrectificd.

It will be noted that the speed regulation is exceptional over theentire speed and load range and even up to overloads of 50% or more. Atno load, however, there is a slight overspeeding. This no load conditionis directly related to the characteristics of this system at the knee ofthe saturation curve; i.e., inductance L is going through a rapid changein magnitude as it approaches the process of becoming unsaturated. Ithas been found that a very small increase in motor load or even a smallsecondary electrical load such as a 50 Watt bulbin parallel with thearmature circuit substantially eliminates the overspeeding condition.

The theoretical principles in FIG. 4 are in general similar to FIG. 1,except that the use of a vector diagram has perhaps somewhat lesstheoretical justification. At constant speed, the counter of the motoris constant, and since the rectified current is variable over the AC.power cycle, the current flow to the motor occurs in the form of pulsesat double the line frequency. It has been found in practice, however,that such pulses have no detrimental effect, and exceptionally closespeed regulation can be obtained over a wide range of load for any givenspeed setting, and the speed may readily be varied over a wide range atwill.

The change of V at all ranges of speed in both the FIG. 1 and FIG. 4systems is practically instantaneous with the change in load. The actualtime lag is in the time range of approximately one-half cycle of linefrequency.

In either form of system, whether series motor or separately-excitedmotor, constancy of speed is obtained without the use of moving parts ordelicate components, and the variations in speed settings are obtainedby simple and inexpensive equipment.

While the systems herein described are inherently stable over a Widerange of inductance, capacitance, and input voltage over a wide range ofelectrical load, whereby transitions in the value of the load effectsmooth and instantaneous transitions in the variable parameters Withoutinstability, it is possible to get into the instability range if onetries to operate these systems at or slightly below the knee of thesaturation curve.

It will be understood that, while the invention has been described withparticular reference to preferred embodiments thereof, various othermodifications of the circuit and structural details can be accomplishedby one skilled in this art without departing from the spirit or scope ofthe invention.

Having thus described the invention, 1 claim:

1. Apparatus for automatically regulating the speed of a motor having incombination a source of alternating- '7 current power, and inductancehaving a substantially saturated core at currents in the normal range ofoperation, a capacitance, a motor, and connections to join the powersource, the inductance, the capacitance and said motor in series.

2. The combination of a source of alternating-current power, andinductance having a substantially saturated core at currents in thenormal range of operation, a capacitance, a motor having a field windingin series with an armature winding, and connections to join the powersource, the inductance, the capacitance and said motor in series.

3. The combination of a source of alternating-current power, aninductance having a substantially Saturated core at currents in thenormal range of operation, a capacitance, rectifier means having itsalternating-current terminals connected between the motor terminals, amotor having a field winding and an armature winding connected in seriesbetween the direct-current terminals of the rectifier means, andconnections to join the power source, the inductance, the capacitanceand said motor terminals in series.

4. An alternating current operated power device compensated for load andhaving a circuit for connection between a pair of terminals across whichan alternating voltage is applied, said circuit having, in seriesconnection, a capacitance, a saturable core inductance and a loadelement, the load element having an effective impedance which varieswith load to cause the current in said circuit to vary between a no-loadvalue and a maximum-load value, the inductance having a core which issubstantially saturated throughout the current range.

5. An alternating current-operated power device cornpensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having, inseriesconnection, a capacitance, a saturable core inductance and a loadelement, the load element having an effective impedance which varieswith load to cause the current in said circuit to vary between a no-loadvalue and a maximum-load value, the core of the inductance beingsubstantially saturated throughout the current range between saidvalues, and said capacitance having a value sufficient to produce apredetermined change in the volt age drop across the load elementbetween the limits of said range.

6. An alternating current-operated motor circuit com-- pensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having, in seriesconnection, a capacitance, a saturable core inductance and the armatureof a motor, and the inductance having a core which is substantiallyfully saturated throughout the current range from the no-load tofull-load values.

7. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich 'an alternating voltage is applied, said circuit having, in seriesconnection, a capacitance, a saturable core inductance and the armatureof a motor, and a separately-excited field for the motor, the inductancehaving a core which is substantially fully saturated throughout thecurrent range from the noload to full-load values.

8. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having, in seriesconnection, a capacitance, a saturable core inductance and rectifyingmeans, a motor having its armature connected to be energized by currentfrom the rectifying means, and means for separately exciting the motorfield, the inductance having a core which is substantially fullysaturated throughout the current range from the no-load to full-loadvalues.

. 9. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having, in seriesconnection, a capacitance, a saturable core reactor and a bridgetyperectifier, a direct-current motor having its armature connected acrossthe rectifier, and means for separately exciting the motor field, theinductance having a core which is substantially fully saturatedthroughout the current range from the no-load to full-load values.

10. The combination according to claim 8, in which the inductance isvariable to change the speed setting.

11. The combination according to claim 8, in which the voltage appliedto said terminals is variable to vary the speed setting.

12. Apparatus according to claim 7, in which the inductance andcapacitance are of such values that the voltage across the inductance isgreater than the voltage across the capacitance throughout the operatingrange of the motor.

13. Apparatus according to claim 8, in which the inductance andcapacitance are of such values that the voltage across the inductance isgreater than the voltage across the capacitance throughout the operatingrange of the motor.

14. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, s-aid circuit having asaturable reactor which has an approximately constant voltage dropacross it over a range of current therethrough, a capacitance in serieswith the reactor, and a motor armature energized by current through saidreactor and capacitance.

15. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having a saturablereactor, means for varying the impedance of the reactor, the reactorhaving, for any given inductance setting, an approximately constantvoltage drop across it over a range of current therethrough, acapacitance in series with the reactor, and a motor armature energizedby current through said reactor and capacitance.

16. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having a saturablereactor, means for varying the number of turns of the reactor, thereactor having, for any given number of turns, an approximately constantvoltage drop across it over a range of current therethrough, acapacitance in series with the reactor, and a motor armature energizedby current through said reactor and capacitance.

17; An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having a saturablereactor which has an approximately constant voltage drop across it overa range of current therethrough, variable transformer means for varyingthe voltage across said pair of terminals, a capacitance in series withthe reactor,

a motor armature energized by current through said reactor andcapacitance.

18. An alternating current-operated motor circuit compensated for loadand having a circuit for connection between a pair of terminals acrosswhich an alternating voltage is applied, said circuit having a saturablereactor, means for varying the impedance of the reactor, the reactorhaving, for any given inductance setting, an approximately constantvoltage drop across it over a range of current therethrough, variabletransformer means for varying the voltage across said pair of terminals,a capacitance in series with the reactor, a motor armature energized bycurrent through said reactor and capacitance, and a connection to causesimultaneous variation of said impedance and transformer.

transformer and reactor to cause simultaneous variation of thetransformer voltage and the number of turns of the reactor.

References Cited in the file of this patent UNITED STATES PATENTSHolliday Dec. 16, 1919 Suits Mar. 12, 1935

1. APPARATUS FOR AUTOMATICALLY REGULATING THE SPEED OF A MOTOR HAVING INCOMBINATION A SOURCE OF ALTERNATINGCURRENT POWER, AND INDUCTANCE HAVINGA SUBSTANTIALLY SATURATED CORE AT CURRENTS IN THE NORMAL RANGE OFOPERATION, A CAPACITANCE, A MOTOR, AND CONNECTIONS TO JOIN THE POWERSOURCE, THE INDUCTANCE, THE CAPACITANCE AND SAID MOTOR IN SERIES.